'Tis the season for night-shining clouds over the Arctic

Earth from spaceThese ghostly high altitude shrouds are rare noctilucent or "night-shining" clouds.

Taken by astronauts on the International Space Station on 8 June, the image shows the clouds illuminated from underneath by the light from the sun setting below the horizon.

Also known as polar mesospheric clouds, these tenuous electric blue glowing wisps are the Earth's highest altitude clouds, forming in the mesosphere near the edge of space, about 75 to 85 kilometres above sea level.

Noctilucent clouds are created as the lower atmosphere warms and the upper atmosphere gets cooler, forming ice crystals on particulate matter such as dust, suspended in the rarefied air.

Noctilucent clouds usually form in the late spring and summer in the higher latitudes between 50° and 70° north and south of the equator.

However, scientists are finding the clouds are both appearing earlier, and stretching to lower latitudes with greater frequency. According to NASA, evidence is pointing to an increase in atmospheric greenhouse gasses as the cause.

The image below is the latest view of the clouds taken by several satellite passes over the Arctic by NASA's Aeronomy of Ice in the Mesosphere or AIM spacecraft from an altitude of about 555 kilometres on June 30, 2015.

The clouds appear in various shades of light blue to white, depending on the density of the ice particles.

(Source: LASP/University of Colorado

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